Amazon could be responsible for nearly half of US e-commerce sales in 2017

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For online retailers, Amazon is becoming even more daunting.

Amazon will own a bigger piece of e-commerce sales this year owning about 44 cents out of every e-commerce dollar spent in the U.S., up from 38 cents the previous year, according to new estimates on public companies from research firm eMarketer.

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Amazon's e-commerce sales are expected to grow 32 percent to $196.8 billion dollars in 2017 in the U.S., or 43.5 percent of total e-commerce sales. These figures represents gross merchandise volume data, which includes sales made by third parties on Amazon's marketplace.

Amazon held 38 percent market share, or $149 billion in sales, in 2016, and it remains the biggest e-commerce company. It is followed distantly by eBay, Apple and Walmart.

Note that this data doesn't include sales from private companies like Stitch Fix, the personal styling online retailer that filed to go public last week, so these companies' true market share is likely smaller.

E-commerce sales are a small but rapidly growing share of U.S. retail, and Amazon is by far the leader. Amazon now represents close to 4 percent of all retail sales online and off in the U.S., according to eMarketer. E-commerce sales will increase 15.8 percent to $452.8 billion by the end of 2017, according to the research firm's estimates.

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This article originally appeared on Recode.